Effects of Na2O/SiO2 molar ratio on properties of aggregate-paste interphase in fly ash-based geopolymer mixtures through multiscale measurements. (10th December 2018)

• Record Type: Journal Article
• Authors: Khedmati, Mahdieh; Alanazi, Hani; Kim, Yong-Rak; Nsengiyumva, Gabriel; Moussavi, Sussan
• Is Part Of: Construction & building materials. Volume 191(2018)
• Page Start: 564
• Page End: 574
• Publication Date: 2018-12-10
• Subjects: Fly ash-based geopolymer -- Interphase -- Nanomechanical properties -- Microstructure -- Multiscale -- Na2O/SiO2 molar ratio; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2018.10.024
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: The effects of Na2 O/SiO2 molar ratio on the interphase of geopolymer was studied. The interphase presents more N-A-S-H gel than adjacent paste regardless of the Na2 O/SiO2 ratios (0.8 and 1.6) attempted. The higher Na2 O/SiO2 ratio led to increased interphase bonding between aggregate and paste. Mechanical and microstructural characteristics in different length scales were in good agreement. Abstract: This paper presents a multiscale experimental study on the influence of different Na2 O/SiO2 molar ratios on the mechanical and microstructural characteristics of the aggregate-paste interphase in fly ash-based geopolymer mixtures. By analyzing the scanning electron microscope images, the solid phases present in the microstructure were identified, and the frequency of occurrence of each phase was quantified. In addition, the porosity and pore size distribution of geopolymer specimens were measured by mercury intrusion porosimetry. By conducting nanoindentation tests on a large array of indentations and subsequent statistical analysis of the test results, the elastic moduli of individual phases were extracted. The bond behavior between aggregate and paste was also investigated by conducting the three-point bending test of single edge notched beam specimens. Integration of test results in different length scales showed that interphase region generates more sodium aluminosilicate hydrate (i.e., N-A-S-H) gel than the adjacent paste region regardless of the Na2 O/SiO2 ratios used in this study. In addition, the mixture prepared with the higher Na2 O/SiO2 molar ratio exhibited more N-A-S-H gel in the interphase zone, which led to increased bonding strength between aggregate and paste.